Isaac Newton, a man of science and religion

In terms of his scientific work, Newton’s most important, long lasting book is the Principia Mathematica or The Mathematical Principles of Natural Philosophy. It's still important because it contains all the basic rules of physics that we still employ for life on Earth and out in space, although it's not very helpful for the subatomic world of quantum physics. But for ordinary life – even for building a spaceship – Newtonian physics is what we still use.

He summarised his thinking in his major work, Principia Mathematica, which is not written in calculus. He used the language of geometry because he believed that that was the great language of the Greeks, and that nothing had surpassed it.

There are several aspects to the Principia. He starts by laying down the basic laws of mechanics. There are three basic laws which we still use in the most elementary calculations. The most important is the third, which introduces a new entity: force, which is mass times acceleration.

In terms of astronomy, the most important aspect of the Principia is showing that comets go around the sun in ellipses, just like planets. There's only one big fold-out diagram in his book and that shows a picture of the sun and then a diagram of a comet that went round the back of the sun and came out the other side again. Before then, the most popular theory was that comets, planets and indeed the universe were all held together by magnetism. But by observing the comet, Newton proved that it didn't go towards the sun and bounce back again. On the contrary, it went round the back just like a planet.

The first revolutionary idea in the Principia was to show that the same laws exist on Earth as throughout the rest of the universe. Before then, dating back to the Greeks and Aristotle, the universe was divided into two basic zones. There was what happened up in the heavens, where all was perfection and order because that was God's realm. Everything moved in circles and there was a single, very fine spiritual ether that pervaded what we now think of as empty space. Down on earth, the laws of nature were very different. There were only four elements – earth, air, fire and water – and everything was movement, corruption and degeneration.

So there were two distinct spheres of the universe. Building on a couple of hundred years of research, Newton contradicted that by saying, no, there is just one law that governs the universe. The force that makes an apple fall to the ground from its tree is the same force that makes the earth go round the sun.

The second revolutionary aspect of Newton's Principia was that he made the universe mathematical. That, I think, was the most fundamental change. He introduced the idea that you can express everything quantitatively. You can set up equations to describe not only the way that the planets go around the sun but also the way that living beings operate and human systems work. This fundamentally quantitative approach to the universe is something that we still have and it's very much Newtonian.

In many ways, Newton's view of the universe was completely different from ours. He's often credited with eliminating God, but that's completely wrong. He was a deeply religious man. God was crucial for him. For Newton, the whole point of studying nature was to get closer to God.

He believed in a universe that was alchemical and alive. His alchemical studies weren't just eccentric experiments carried out by someone who was reclusive and a bit mad. They were central to some of the theories he had about natural philosophy. He suggested that in this living universe, God intervenes from time to time, sending a comet with live vegetative matter in its tail to somehow restore the equilibrium of the earth.

That’s something he was much criticised for. His great rival, Gottfried Leibniz, who competed with Newton to be recognised as the inventor of calculus, dismissed Newton’s notion of God. He thought it was as though Newton's God were a sloppy clockmaker, who couldn't wind up his clock at the beginning of the universe and set it going. He has to keep winding it up from time to time. So, our version of Newton is rather different from the one that Newton himself put forward.

Going back to Newton's monument in Westminster Abbey, he's reclining his elbow on four books – one on gravity, another on optics and another two on theology and ancient chronology that we don’t know much about now.

Because the world has become so scientific, we tend to focus on the parts of Newton's work that seem important to us. But as far as he and his contemporaries were concerned, his other areas of scholarship were just as important. In theology, for instance, he owned about 30 Bibles, one of which still exists in the university library at Cambridge. You can see by the way the pages are thumbed and dog-eared that his favourite book was the Book of Daniel.

He wrote a lot about theology, biblical interpretation and King Solomon's temple. And he also wrote about what he called ancient chronology: the idea of redating ancient kingdoms such as those of the Egyptians and the Babylonians. You can do that through astronomy: just as Newton could use astronomy to predict an event in the future, he could use the same theory to work out exactly when an eclipse or some other sort of astronomical event happened in the past.